A review of Secondary Organic Aerosol (SOA) formation from isoprene

Abstract

Abstract. Recent field and laboratory evidence indicates that the oxidation of isoprene, (2-methyl-1,3-butadiene, C 5 H 8 ) forms secondary organic aerosol (SOA). Global biogenic emissions of isoprene (600 Tg yr −1 ) are sufficiently large that the formation of SOA in even small yields results in substantial production of atmospheric particulate matter, likely having implications for air quality and climate. Here we present a review of field measurements, experimental work, and modeling studies aimed at understanding the mechanisms, yield, and atmospheric importance of isoprene-derived SOA. SOA yields depend on a number of factors, including organic aerosol loading (M o ), NO x level (RO 2 chemistry), and, because of the importance of multigenerational chemistry, the degree of oxidation. These dependences are not always included in SOA modules used in atmospheric transport models, and instead most yield parameterizations rely on a single set of chamber experiments (carried out over a limited range of conditions); this may lead to very different estimates of the atmospheric importance of isoprene SOA. New yield parameterizations, based on all available laboratory data (M o =0-50 µg m −3 ), are presented here, so that SOA formation may be computed as a function of M o , NO x level, and temperature. Current research needs and future research directions are identified.

Observational Insights into Aerosol Formation from Isoprene

“…10 In the atmosphere, isoprene reacts predominantly with OH 11 forming SOA with a yield of 1−4% under low NO x (NO x < 0.1 ppb), 12 1−6% under high NO x (NO x > 1 ppb), 13,14 and up to 29% in the presence of highly acidic seed aerosols, 15 making it an important source of SOA. In smog chamber experiments, SOA yields were observed to be dependent on NO x concentrations, the VOC/NO x ratio, the NO 2 /NO ratio and aerosol acidity, 7,9,13,15 consistent with an anthropogenic−biogenic coupling.…”

“…5,6 Several probable explanations for the anthropogenic enhancement of biogenic SOA have been suggested: (i) enhanced gas to particle partitioning of semivolatile oxidation products onto pre-existing anthropogenic primary and secondary particles, 5 (ii) enhanced uptake of reactive species by acidic aerosols, 7 (iii) oxidation by the nitrate radical (NO 3 ), 8 and (iv) influence of nitrogen oxide (NO x = NO + NO 2 ) concentrations on both SOA yields and enhancing oxidant (i.e., hydroxyl radical; OH) concentrations. 5,9 Isoprene is emitted from vegetation and is the single largest source of VOCs to the atmosphere with global emissions of ∼500 Tg C yr −1 . 10 In the atmosphere, isoprene reacts predominantly with OH 11 forming SOA with a yield of 1−4% under low NO x (NO x < 0.1 ppb), 12 1−6% under high NO x (NO x > 1 ppb), 13,14 and up to 29% in the presence of highly acidic seed aerosols, 15 making it an important source of SOA.…”

Canopy level emissions of 2-methyl-3-buten-2-ol, monoterpenes, and sesquiterpenes from an experimental Pinus taeda plantation

“…Over 80% of new plantations are established with genetically improved P. taeda seedlings (McKeand et al, 2003), produced via controlled pollination, cloning, and tissue culture, with the goals of improving biomass production, stem/fiber quality, crown characteristics, and disease resistance. Since the southeastern U.S. has persistent PM 2.5 and O 3 air quality problems that are complicated by BVOC emissions (Carlton et al, 2009;Trainer et al, 1987), it is important to improve understanding of BVOC fluxes from P. taeda, characterize BVOC emission model performance, and examine effects such as genetic and regional variability on BVOC emissions.…”

“…Based on published sesquiterpene aerosol yields and branch enclosure measurements from P. taeda, Helmig et al (2006) determined that sesquiterpenes can significantly impact secondary organic aerosol (SOA) concentrations in the southeastern U.S. Carlton et al (2009) conclude that "Global biogenic emissions of isoprene (600 Tg yr −1 ) are sufficiently large that the formation of SOA in even small yields results in substantial production of atmospheric particulate matter, likely having implications for air quality and climate". The compound 2-methyl-3-buten-2-ol (MBO) has also been found to contribute to the chemistry of SOA and tropospheric ozone in the western United States (Jaoui et al, 2011;Steiner et al, 2007).…”

In vitro exposure to isoprene-derived secondary organic aerosol by direct deposition and its effects on &lt;i&gt;COX-2&lt;/i&gt; and &lt;i&gt;IL-8&lt;/i&gt; gene expression

“…Isoprene SOA comprises a large portion of global atmospheric fine particles (PM 2.5 , aerosol with aerodynamic diameters ≤ 2.5 µm) (Carlton et al, 2009;Henze et al, 2008), but few studies have focused on its health implications . Evaluating the health effects of SOA from isoprene oxidation is important from a public health perspective, not only because of its atmospheric abundance but also because the anthropogenic contribution is the only component amenable to control (Pye et al, 2013;Gaston et al, 2014;Xu et al, 2015;Riedel et al, 2015).…”